KR100684182B1 - A method of making an element of a liquid crystal polymer, an element of a liquid crystal polymer made by the method and an optical device comprising the element - Google Patents

Abstract

A method of imparting a property to a material, the property being that cross-linkable monomeric or pre-polymeric liquid crystal molecules which may be placed on the layer would adopt preferred alignment. The method comprises exposing the material to unpolarised or circularly polarised radiation from an oblique direction, wherein the material is, for example, cross-linked by the irradiation, allowing monomeric or pre-polymeric liquid crystal molecules applied to or mixed with the exposed material to adopt the preferred alignment and while aligned cross-linking them. The invention also relates to LCD elements incorporating a preferred alignment.

Description

A method of making an element of a liquid crystal polymer, an element of a liquid crystal polymer made by the method and an optical device comprising the element}

The present invention relates to a method of imparting to a layer a property in which liquid crystal molecules which can be positioned above the layer adopt the desired alignment properties. The invention also relates to an LCD device which is preferably aligned.

For the operation of liquid crystal devices (e.g. liquid crystal displays and light valves, and liquid crystal polymer elements such as optical retarders, polarizers, cholesteric filters, etc.), the controlled alignment and, in general, also the pretilt of the liquid crystal need. Conventionally, mechanical friction techniques have been used to produce surfaces that can induce alignment and pretilt.

In order to solve the shortcomings of the friction technique, a number of optical methods have been developed that use linear polarization and are commonly referred to as photo-alignment methods. These are described in US Pat. 0525478B.

They are satisfactory themselves, but the methods described in these patent documents rely on polarization. Light sources that provide polarization are relatively complex, which may be less suitable for mass production and expensive. Since polarizers generally absorb more than 50% of light, distributing them to polarizers may make the light source more useful (quick effect or weaker lamps). Thus, certain methods have already been proposed, which use unpolarized light sources.

A method of generating a pretilt angle of a nematic liquid crystal cell using a polyimide surface irradiated with unpolarized ultraviolet light having an angle of incidence of 70 ° to the surface normal is described in Seo et al in "Asia Display 98" paper P- 81, pp 795-798 and "Liquid Crystals", 1997 vol 23 no. 6 pp 923-925. However, this method does not provide the potential benefits identified by the inventors and instead requires very high energy inputs sufficient to depolymerize the polyimide.

It has been found by the present invention that under certain unforeseen circumstances, the above-mentioned optical light-alignment method is also operated by light that is nonlinearly polarized (eg circularly polarized) or isotropic (not polarized).

According to the present invention, there is provided a process for producing a liquid crystal polymer device, comprising imparting to the material the property that the crosslinkable monomeric or prepolymeric liquid crystal molecules located on the layer of material or composite material adopt the desired alignment. Exposing the materials to unpolarized or circularly polarized radiation from the oblique direction and to crosslinking them while applying or mixing monomeric or prepolymeric liquid crystal molecules to the exposed material to adopt the desired alignment. Provided are methods for inclusion.

Preferably, the angle of incidence (psi) of the radiation with respect to the normal of the layer is greater than 5 ° ≦ ψ <70 °, more preferably 45 °.

The radiation may be ultraviolet light.

The above preferred alignment is preferably in a plane in which the longitudinal axis of the liquid crystal molecules comprises a layer and the normal to the radiation direction. The alignment may be planar (0 °) or inclined (90 ° or less). The preferred tilt imparted is preferably greater than 45 ° with respect to the plane of the layer, more preferably greater than 75 °.

In addition, the effect of radiation on the material can crosslink the material and also improve the stability of the material and its alignment properties.

For radiation to which the material is exposed, this is the preferred alignment of the above characteristics, for example by inserting a microelement array such as a microlens or microprism array or a suitable hologram element between the radiation source and the material and patterning by area. This area can be patterned. Using such microelement arrays, it is also possible to generate different oblique radiation in position from a single radiation source even if the radiation source itself is irradiated in a direction perpendicular to the material layer or the microelement array.

In this method, when radiation is used for non-polarization, preferably ultraviolet and suitable alignment layer materials of a certain roughness geometry, the isotropic layer is converted to an anisotropic layer prior to irradiation. The layers and methods typically have the following unique characteristics:

After (a) conversion, the layer has an alignment effect on the monomeric or prepolymeric liquid crystal material applied on the layer.

Simultaneously with the development of anisotropy in layer (b), crosslinking also occurs. That is, the generation of alignment ability and crosslinking is based on a bimolecular light process, but the method according to the invention can also be applied to single molecule processes which typically use azo dyes.

Preferably, if the light-alignment sensitivity of the material layer is better than ² J / cm ² and the irradiation energy (measured in the direction perpendicular to the radiation) can be kept correspondingly below ² J / cm ² , the exposure time is Productivity is improved because it can be shortened to less than 10 minutes.

The layers can be structured by light. That is, the azimuth alignment and tilt angle may be different for different parts of the layer (e.g. exposure through a photomask, holographic imaging, microprisms, microlenses, and pixelated optical switches such as micro-mirrors). By imaging).

On the other hand, devices which are uniformly aligned over a large area, in particular LCP retardation plates and optical compensation plates for improving the viewing angle of the display, may also be manufactured by the method.

These layers can be used as alignment layers for liquid crystal devices such as displays; The display may contain monomeric nematic, cholesteric or smectic (including chiral smectic C) liquid crystals. The mode of operation can be transmissive or reflective. In reflection, both reflective metallic or diffuse reflecting plates can be used, as well as reflecting plates made of cholesteric layers or polarization converting optical elements such as BEF foils.

The device substrate may be glass, plastic, silicon chip or any other suitable.

The advantage of not needing to use polarization, in addition to those already described above, generally simplifies the method, makes the method more suitable for mass production, and is not possible by polarization, in just one irradiation step. The use of microlenses-, microprisms- or similar arrays of illumination, leading to structured alignment.

The present invention relates to a vertically aligned nematic (VAN) cell in which the angle of inclination of the liquid crystal display with respect to two surfaces is 90 ° ≥θ> 75 °, or the angle of inclination with respect to one surface is 90 ° ≥θ ₁ > 75 ° and the other surface It can be used in conjunction with a hybrid aligned nematic (HAN) cell with an inclination angle for θ ₂ ≦ 30 °. Intermediate tilt angles on one or both surfaces may also have utility.

The material as such can be substantially homeotropically oriented. That is, the material herein may be one that induces a large tilt angle (not oriented to azimuth) that is not necessarily exactly 90 ° to the liquid crystal molecules, but preferably exceeds 80 ° and more preferably exceeds 85 °. . In particular, where a large tilt angle is required, it may be advantageous to start with a substantially homeotropic alignment material that requires only minor adjustments of the derived tilt angle to achieve exactly the required tilt (except for isotropic alignment).

The materials used in the present invention may be photopolymerizable polymers, in particular linear photopolymerizable polymers, such as those also used in known photo-alignment methods.

Materials used in this way may include photopolymerizable polymers, as well as monomolecular alignment materials that are inherently unstable because photo-alignment does not crosslink them. If the single molecular material is photo-aligned and the liquid crystal polymer layer is applied, the liquid crystal polymer itself can be crosslinked (stabilized at the aligned position), so it is irrelevant because the instability of the single molecular material has no damaging effect .

The invention is also applicable to photopolymerizable mixtures comprising liquid crystal monomers or prepolymers (i) having crosslinkable groups and photoalignable monomers or oligomers or polymers (ii). Such mixtures are described in British Patent Application No. 9812636.0, incorporated herein by reference. Despite the pronounced action of the molecules involved, these mixtures can be oriented and crosslinked in the liquid crystal polymer. Therefore, these mixtures are useful on the one hand as anisotropic layers of optical members, and on the other hand generally thinner as oriented layers.

Material (i) may also be a liquid crystalline polymer mixture. That is, it is understood that it can contain two or more different liquid crystalline molecular forms. Equivalently, the material (ii) may be a mixture of photoalignable molecules. Assuming that the crosslinkable liquid crystal material (i) is present in an amount of 100 parts, the photo-alignable material (ii) is preferably in an amount of at least 0.1 part, more preferably at least 1 part, most preferably at least 10 parts. exist. Preferred photo-orientable materials (ii) comprise molecules exhibiting cis-trans isomerism, in particular azo dyes. Another preferred photoalignable material (ii) comprises a photopolymerizable polymer linearly. Depending on the intended use, the crosslinkable liquid crystal material (i) may have a nematic phase or a cholesteric phase or a ferroelectric phase, respectively. The material (s) (i) are preferably acrylates or diacrylates. The mixture may also comprise chiral molecules or dye molecules or dichroic molecules or fluorescent molecules.

The present invention extends to devices made from liquid crystal polymers by the method described above. Such devices may advantageously comprise a number of cross-linked liquid crystal polymer layers (or mixtures thereof) applied and aligned sequentially.

The present invention also extends to an optical device comprising the above-described device (e.g., optical device), which relies on a liquid crystal polymer having fixed properties. Examples of such devices would include alignment layers, optical retardation plates, polarizers, cholesteric filters, or devices for protecting documents from radiation or modulation.

The invention will be described by the following examples.

Example 1 Vertically Aligned Nematic (VAN) Cells

A 2% solution S1 of photopolymer A in cyclopentanone was prepared and stirred at room temperature for 30 minutes.

Photopolymer A:

Solution S1 was spin-coated on two indium tin oxide glass plate substrates at a rate of 2000 rpm and then dried at 130 ° C. on a hot plate for 30 minutes. All these operations were performed under reduced ultraviolet light environment.

The coated substrate was then exposed to isotropic ultraviolet light from a 200 W high pressure mercury lamp for 6 minutes at an incident angle of 65 ° to the normal of the substrate. One edge of each substrate was arranged parallel to the substrate and a plane having a normal direction to incident light during exposure.

Use the UV edge filter WG295 (Schott) and the bandpass filter UG11 (Scott) to limit the band width of the light and use a photometer 1000 (Carl Suss) with a probe set to 320 nm Thus, it was found that the intensity of light measured on the substrate (indicating the normal direction to incident light) was ² nW / cm ² . Cells with parallel faces were assembled using two substrates, which are coatings facing each other, and spaced at 2.7 μm using plastic wedges. Subsequently, at room temperature, the Swiss Roquel Rezearich Limited (Rolic) has a dielectric anisotropy (Δε) of -3.5, an optical anisotropy (Δn) of 0.096 and a liquid crystal-isotropic transition temperature (T _c ) of 77.3 ° C. "Liquid Crystal Mixture 8987" commercially available from Research Ltd. was charged.

When the cell was viewed between crossed polarizers, it appeared dark at all azimuth angles of the cell with respect to the polarizer. That is, the liquid crystal mixture was homeotropic.

When 5V 90Hz is applied between the electrodes of the substrate, (i) the cell transmits the light maximally when its edge is arranged at 45 ° with respect to the polarization direction of the crossed polarizers, and (ii) the cell has its edge When arranged so as to be parallel and perpendicular to the polarization direction of the crossed polarizers, it darkened to the maximum. This demonstrates that the liquid crystal mixture is oriented according to the plane of incidence of the original layer-irradiated light, which is considered parallel to the edge of the substrate and thus also to the edge of the cell.

Using the tilt compensation plate, it is demonstrated that the optical axis of the switched liquid crystal is parallel to the line of the intersection of the substrate and the original incident surface which irradiates ultraviolet rays.

Repeating the application of alternating current with a potential difference of only 3 V under visual condition (i), the cell exhibited only weak permeability, which is seen perpendicular to its plane. In other words, the liquid crystal director η only tilted slightly. To ascertain the direction of inclination of the liquid crystal, the cell was inclined until it became dark again with respect to the axis laid in the plane of the cell perpendicular to the plane containing η. In this orientation, the cell was effectively seen along the optical axis, i. This indicates that the inclination direction of the liquid crystal relative to the normal direction of the cell is the reverse direction of the incident direction of the original ultraviolet irradiation.

With or without an applied voltage, the orientation of the liquid crystal was uniform without potential or domain boundaries. In particular, during switching, no so-called reverse gradient domains occurred at all, such as occur when the liquid crystal molecules are reversely inclined in some regions through too small inclination angles in the alignment layer.

Example 2 Preliminary Incline Measurement

As in Example 1, two ITO coated glass plates were spin coated with a S1 solution and dried at 130 ° C. for 30 minutes.

Subsequently, the two substrates were exposed to isotropic ultraviolet rays having an incident angle of 65 ° with respect to the normal direction of the substrate for 6 minutes. The spectral range of light was limited by the UV cut filter WG295 (Scott) and band filter UG11 (Scott). The intensity of the ultraviolet light at the location of the photosensitive layer was measured at ² mW / cm ² using a Karl Sheath optical intensity measuring device with a 320 nm probe (Carles sheath).

In order to measure the pretilt angle induced by the alignment layer, parallel cells were assembled with the illumination substrate. The cell gap was set to 20 mu m using two quartz fibers as spacers. The cell is negative dielectric liquid crystal mixture with dielectric anisotropy of -5.1, optical anisotropy (Δn) of 0.0984 and liquid crystal-isotropic transition temperature (T _c ) of 75.8 ° C. (mix 9383, manufactured by Rolik Rezearich, Switzerland). Before filling with the cell, the cell was heated to 90 ° C. to carry out a filling process on the isotropic phase of the liquid crystal mixture. After filling, the cells were cooled to room temperature at a rate of 1 ° C./min.

For the measurement of the pretilt angle, a crystal rotation method was used. As a result of the measurement, it was found that the liquid crystal director was inclined 3 ° from the substrate normal.

Example 3-Liquid Crystal Polymer (LCP) Member

First, 2 wt% solution (S2) of the light alignment material (B) was prepared using cyclopentanone as a solvent. The solution was stirred at rt for 30 min.

Polymer B:

A mixture M _{LCP was} then prepared comprising the following liquid crystalline diacrylate monomers:

Monomer 1:

Monomer 2:

Monomer 3:

In addition to the diacrylate monomers, BHT (2,6-di-tert-butyl-4-methylphenol / "butyl hydroxytoluene") acts as an inhibitor, as well as photoinitiators Irga purchased from Ciba SC. IRGACURE 369 was added to the mixture. Thus, the composition of the mixture M _LCP is as follows:

Monomer 1 77 wt%

Monomer 2 14.5 wt%

Monomer 3 4.7 wt%

Irgacure 369 1.9% by weight

1.9 wt% BHT.

Finally, solution S (LCP) was formed by dissolving 10% by weight of the mixture M _{LCP in} anisole.

Preparation of the layer was initiated with spin coating solution (S2) on a rectangular glass substrate 1 mm thick at 3000 rpm for 1 minute as a rotational parameter. The layer was then dried at 130 ° C. on a hotplate for 30 minutes.

The coated substrate was then exposed to isotropic ultraviolet light of a 200 W high pressure mercury lamp with an incident angle of 65 ° to the substrate normal for 6 minutes. The incident surface of ultraviolet light defined by the substrate normal and the direction of light incidence was aligned parallel to the longer edge of the substrate. The spectral range of light was limited by the UV cut filter WG295 (Scott) and band filter UG11 (Scott). The intensity of the ultraviolet light at the location of the photosensitive layer was measured to be ² mW / cm ² using a Karl Sheath light intensity measuring device with a 320 nm probe (Karls sheath).

When the substrates were arranged between crossed polarizers, the substrate appeared dark regardless of the angle between the substrate edge and the polarizer transmission axis. As a result, there was no appreciable birefringence induced in the photosensitive layer.

As a next step, an M _LCP layer was prepared on top of the ultraviolet exposed photosensitive layer by spin coating at 1000 rpm for 2 minutes with coating solution (S) (LCP). Subsequently, the substrate was _removed from the mixture M _LCP It heated to 70 degrees C or less slightly higher than 68 degreeC which is a clear point _Tc , and cooled to 65 degreeC at the cooling rate of 0.1 degree-C / min. The M _LCP layer was then crosslinked under a nitrogen atmosphere by exposing it to the light of a 150 W xenon lamp for 10 minutes. The thickness of the crosslinked M _LCP layer was measured at 250 nm.

When the substrate was arranged between polarizers crossed at a 45 ° angle between the substrate edge and the transmission axis of the polarizer, the substrate appeared gray. However, when its edges were arranged parallel or perpendicular to the transmission axis of the polarizer, the substrate appeared dark. As a result, the M _LCP layer was birefringent with respect to the optical axis aligned parallel or perpendicular to the longer substrate edge. However, by the tilt compensation plate, the optical axis of the M _LCP layer was found to be parallel to the longer substrate edge, which is arranged parallel to the plane of incidence of the ultraviolet rays during illumination of the light alignment material JP 265.

In addition to the azimuth alignment, the present invention has found that the optical axis of the M _LCP layer is inclined relative to the substrate surface at an average tilt angle of about 30 ° with respect to the substrate plane. From the viewing angle dependence of the optical appearance, it was concluded that the optical axis in the M _LCP layer was inclined opposite to the direction of incidence of the ultraviolet light used to illuminate the light alignment layer.

Therefore, exposure to oblique incident isotropic ultraviolet light not only uniformly tilts the M _LCP molecules from the layer plane in the alignment layer, but also strong enough to align the liquid crystal monomers of the mixture M _LCP parallel to the plane of incidence of the ultraviolet light. Twill was induced.

Claims (15)

A method of making a liquid crystal polymer device, comprising imparting to the material a property that crosslinkable monomeric or prepolymeric liquid crystal molecules positioned on a layer of material or composite material adopt alignment. Exposing the material to unpolarized or circularly polarized radiation from the oblique direction and crosslinking the alignment while applying or mixing monomeric or prepolymeric liquid crystal molecules to the exposed material to adopt alignment. A method of manufacturing a liquid crystal polymer device, comprising the step. The manufacturing method of the liquid crystal polymer element of Claim 1 whose irradiation energy measured in the perpendicular direction with respect to radiation is less than ² J / cm <^2> . Claim 3 was abandoned when the setup registration fee was paid. The manufacturing method of the liquid crystal polymer element of Claim 1 or 2 whose radiation is an ultraviolet-ray. Claim 4 was abandoned when the registration fee was paid. The method for manufacturing a liquid crystal polymer device according to claim 1 or 2, wherein the alignment is in a plane in which the longitudinal axis of the liquid crystal molecules includes a normal to the layer and the radiation direction. The method of claim 1, wherein the material is oriented substantially homeotropic. Claim 6 was abandoned when the registration fee was paid. The manufacturing method of the liquid crystal polymer element of Claim 1 or 2 whose incident angle (psi) of the radiation with respect to the normal of a layer is 5 degrees <= <70 degrees. Claim 7 was abandoned upon payment of a set-up fee. The manufacturing method of the liquid crystal polymer element of Claim 1 or 2 whose incident angle (psi) of the radiation with respect to the normal of a layer exceeds 45 degrees. The method for producing a liquid crystal polymer device according to claim 1, wherein the material is crosslinked by radiation. The liquid crystal according to claim 1 or 2, further comprising the property of providing tilt as well as azimuthal alignment to the liquid crystal molecules before the liquid crystal molecules are crosslinked to fix the tilt and alignment. Method for producing a polymer device. 3. The liquid crystal polymer according to claim 1, wherein the radiation exposing the material is zonewise patterned so that, in the given properties, the alignment is patterned such that the alignment differs from area to area. Method of manufacturing the device. The method of claim 10, wherein the microelement array is inserted between the radiation source and the material. 3. The method of claim 1, wherein the material comprises a mixture of a liquid crystal monomer or prepolymer having a crosslinkable group with a photo-alignable monomer, oligomer or polymer. A liquid crystal polymer device produced by the method according to claim 1. The device of claim 13, comprising a plurality of liquid crystal polymer layers or mixtures sequentially applied and aligned. A liquid crystal polymer dependent optical device having a fixed property, comprising an element according to claim 13 or 14, comprising an alignment layer, an optical retardation plate, or an element for protecting documents from radiation or modulation.